Alain Chaintreau

Comparison of extraction techniques and modeling of accelerated solvent extraction for the authentication of natural vanilla flavors

Accelerated solvent extraction (ASE) of vanilla beans has been optimized using ethanol as a solvent. A theoretical model is proposed to account for this multistep extraction. This allows the determination, for the first time, of the total amount of analytes initially present in the beans and thus the calculation of recoveries using ASE or any other extraction technique. As a result, ASE and Soxhlet extractions have been determined to be efficient methods, whereas recoveries are modest for maceration techniques and depend on the solvent used. Because industrial extracts are obtained by many different procedures, including maceration in various solvents, authenticating vanilla extracts using quantitative ratios between the amounts of vanilla flavor constituents appears to be unreliable. When authentication techniques based on isotopic ratios are used, ASE is a valid sample preparation technique because it does not induce isotopic fractionation.

Simultaneous distillation—extraction under static vacuum: isolation of volatile compounds at room temperature

Abstract The simultaneous distillation—extraction (SDE) system developed by Likens and Nickerson (ASBC Proceedings, 1964, p. 5) and modified by Godefroot, Sandra and Verzele [J. Chromatogr., 203 (1981) 325] is one of the most popular methods currently used to isolate volatile components from a matrix prior to gas chromatographic analysis. Since it leads to a thermal generation of artefacts, the device has been improved in the present work to allow isolation between 20 and 40°C under vacuum. The system was closed and made airtight by means of a valve under static vacuum to avoid volatile losses. These conditions require the use of solvents with a boiling point close to that of water and the temperature must be electronically regulated. The absence of artefact generation was tested with linalyl acetate, honey and a Maillard model reaction. The recovery yields of classical SDE and SDE under vacuum were found to be similar.

Strategy for the identification of key odorants: Application to shrimp aroma

The GC-SNIF technique was used to obtain the olfactograms of shrimps, and their impact odorants were identified by MS hyphenated to the GC/olfactometric system and by comprehensive two-dimensional GC hyphenated to a time-of-flight MS. Confirming these identifications by their linear retention indices required application of a new strategy to compare retention indices between both instruments and with the in-house database. The aldehydes were confirmed by using their pentafluorophenylhydrazone derivatives, and 2-ethyl-3,5-dimethyl pyrazine had to be resolved from co-eluting compounds and then identified by multidimensional GC hyphenated to an MS and a sniff port. In both shrimp products, the most important odorants were trimethylamine, 2-acetyl-1-pyrroline, and 2-ethyl-3,5-dimethyl pyrazine, together with common carbonyl compounds.

Simultaneous distillation–extraction: preparative recovery of volatiles under mild conditions in batch or continuous operations

In a previous publication, a preparative apparatus was developed and optimized for simultaneous distillation–extraction (SDE) based on a theoretical model. In this paper, its performances were tested under various working conditions using a model mixture of flavourings. Separations were achieved at boiling water temperature as well as under mild conditions, which reduce artefact formation (room temperature, reduced pressure). High recoveries were obtained for batch experiments, but the boiler can also be fed from an external tank for continuous operations. This permits consideration of the preparative isolation of volatiles on a laboratory scale for subsequent fractionation and analysis, as well as industrial scale operations. Examples are given for real food flavours: one-step preparation and isolation of a reaction flavour, isolation of yoghurt and coffee flavourings, recovery of natural benzaldehyde from wastewater. In addition, the use of a food-grade solvent to achieve SDE isolation yields an ‘edible’ extract which can be reincorporated into a food without elimination of the solvent. Copyright

Quantitation of the main constituents of vanilla by reverse phase HPLC and ultra-high-pressure-liquid-chromatography with UV detection: method validation and performance comparison.

Vanillas main constituents, i. e., vanillin, para-hydroxybenzaldehyde, and their corresponding acids, can be easily quantified by RP LC with UV detection and external calibration. This paper describes two methods that were developed using HPLC and ultra-high-pressure LC (UHPLC), respectively, and validated according to the International Conference on Harmonisation of Technical Requirements for Registration of Pharmaceuticals for Human Use (ICH). Both methods were highly specific, exhibited good linearities with high precision, and achieved good accuracies of quantitative results. The UHPLC method was more sensitive, five times shorter, and gave better peak resolutions than the HPLC alternative.

Prediction of response factors for gas chromatography with flame ionization detection: Algorithm improvement, extension to silylated compounds, and application to the quantification of metabolites

We previously showed that the relative response factors of volatile compounds were predictable from either combustion enthalpies or their molecular formulae only 1. We now extend this prediction to silylated derivatives by adding an increment in the ab initio calculation of combustion enthalpies. The accuracy of the experimental relative response factors database was also improved and its population increased to 490 values. In particular, more brominated compounds were measured, and their prediction accuracy was improved by adding a correction factor in the algorithm. The correlation coefficient between predicted and measured values increased from 0.936 to 0.972, leading to a mean prediction accuracy of ± 6%. Thus, 93% of the relative response factors values were predicted with an accuracy of better than ± 10%. The capabilities of the extended algorithm are exemplified by (i) the quick and accurate quantification of hydroxylated metabolites resulting from a biodegradation test after silylation and prediction of their relative response factors, without having the reference substances available; and (ii) the rapid purity determinations of volatile compounds. This study confirms that Gas chromatography with a flame ionization detector and using predicted relative response factors is one of the few techniques that enables quantification of volatile compounds without calibrating the instrument with the pure reference substance.

Good quantification practices of flavours and fragrances by mass spectrometry.

Over the past 15 years, chromatographic techniques with mass spectrometric detection have been increasingly used to monitor the rapidly expanded list of regulated flavour and fragrance ingredients. This trend entails a need for good quantification practices suitable for complex media, especially for multi-analytes. In this article, we present experimental precautions needed to perform the analyses and ways to process the data according to the most recent approaches. This notably includes the identification of analytes during their quantification and method validation, when applied to real matrices, based on accuracy profiles. A brief survey of application studies based on such practices is given. This article is part of the themed issue ‘Quantitative mass spectrometry’.

Effects of variation in modulator temperature during cryogenic modulation in comprehensive two-dimensional gas chromatography.

Many modulation systems in comprehensive 2D GC (GC x GC) are based on cryogenic methods. High trapping temperatures in these systems can result in ineffective trapping of the more volatile compounds, whilst temperatures that are too low can prevent efficient remobilisation of some compounds. To better understand the trapping and release of compounds over a wide range of volatilities, we have investigated a number of different constant temperature modulator settings, and have also examined a constant temperature differential between the cryo-trap and the chromatographic oven. These investigations have led us to modify the temperature regulation capabilities of the longitudinally modulated cryogenic system (LMCS). In contrast to the current system, where the user sets a constant temperature for the cooling chamber, the user now sets the temperature difference between the cryo-trap and the chromatographic oven. In this configuration, the cooling chamber temperature increases during the chromatographic run, tracking the oven temperature ramp. This produces more efficient, volatility-dependent modulation, and increases the range of volatile compounds that can be analysed under optimal trap-and-release conditions within a single analytical run. This system also reduces cryogenic fluid consumption.

Extraction, thermal cleanup, and GC/MS quantification with disposable solid extractants: Application to hydrophobic analytes in aqueous surfactant solutions

Fragranced consumer products are generally formulated together with surfactants. In application, these products are often highly diluted with water. Analyzing trace amounts of fragrance ingredients in such mixtures is challenging and usually requires either time-consuming sample cleanup or extensive cleaning of the trapping device to avoid memory effect and cross-contamination between samples. To overcome these limitations, a new disposable extraction device has been developed to be used in combination with a thermodesorption-GC-MS unit. Made of PDMS foam cylinders, it efficiently extracts trace amounts of hydrophobic compounds from complex aqueous solutions and provides an online sample cleanup, thanks to the controlled desorption temperature, which allows retaining the low volatile constituents of the matrix within the absorptive foam. Combined with a stable isotope dilution assay, accurate quantifications of Cetalox(®), Muscenone™, Helvetolide(®), Polysantol(®), Dartanol, and Myrrhone(®) from aqueous solution containing surfactant and from water from the aeration tank of a sewage plant were successfully conducted. LOQ varied between 1 and 25 ppb (20% confidence interval, α = 0.1).

Novel concept of multidimensional gas chromatography. New capabilities for chiral analysis and olfactometric detection

Abstract In multidiumensional gas chromatography (MDGC), the analyte transfer from the first to the second column is usually achieved using either a valve, or a pneumatic switcher. Both systems have significant drawbacks (degradation of analytes, switchercomplexity, etc.). A new design, based on the double-cool-strand interface (DCSI) overcomes these limitations due to: 1) simplicity and low coest, 2) no degradation of labile compounds, 3) no dead volume, 4) optimised chiral MDGC conditions with a single oven, 5) higher sensitivity and peak resolution. Examples illustrate the suitability of this technique when various detection means are hyphenated to MDGC: FID, mass spectrometry and olfactometric detection. In addition, the use of the new interface in conjunction with a chiral colum allows the odour evaluation of enantiomers with an interval of several minutes. Such a possibility that may not be achieved with previous interfaces, allows the panellist to recover from the first stimuli prior to smelling the second one. This is particularly important for long-lasting compounds, such as mercaptans, as exemplified with 3-methyl-3-mercapto-1-hexanol found in human sweat.